


Multiverse Theory

by SoSaidTheDragon



Category: Undertale (Video Game)
Genre: Absolutely No Fontcest, Alternate Universe - Swapfell, Alternate Universe - Underfell, Alternate Universe - Underswap, F/M, Original Character(s), Possible Other AU to be Added Later, Swapfell Papyrus - Freeform, Underfell Sans, Underswap Papyrus, multiple AUs
Language: English
Status: In-Progress
Published: 2018-06-17
Updated: 2018-06-16
Packaged: 2019-05-24 08:56:45
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,498
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14951571
Author URL: https://archiveofourown.org/users/SoSaidTheDragon/pseuds/SoSaidTheDragon
Summary: A series of oneshots, wherein a lucky character gets all the skeleton she can handle. And then some.





	Multiverse Theory

**Author's Note:**

> Most of the AU I intend to use either have no known author, or the original creator has stepped away for their own reasons. As they've stepped away, I won't be crediting them for the idea, and potentially send people from this work to their blog when they don't want to be involved in anything AU related anymore. There are far too many blogs that currently host these AU, so I really couldn't credit them if I wanted to - there are some major blogs, but there's really no one source anymore. Instead, I'll credit the fandom in general for perpetuating the AUs that I use here, or else I would likely never have heard of them to begin with, and then where would we be?
> 
> Should you be interested in looking up more about these AU, I'll list them below. I'll also say now that the versions you'll see here are my interpretations of the characters from these AU, and may be a far cry from what you'll find, or what you may be used to if you're already familiar. I typically don't follow these AU blogs, and my interpretation is based largely off of stories I've read here as opposed to things like tumblr blogs, and a bit of general knowledge gleaned from my rare forays into the tags on tumblr. To my knowledge, none of the AU I've used or intend to use have active authors, however, I may add more later, and if it turns out that this isn't the case, send me a message here or on my tumblr, Sosaidthedragon, so I can fix it. 
> 
> Undertale - Credit to Toby Fox  
> Underswap (Stretch)  
> Underfell (Red)  
> Swapfell (Rus)

Blanket

The winter had been particularly severe. 

The area where they lived was a little too far south for the winters to be consistently bad, and too far north for them to escape the potential for knee deep snow fall at any moment, although for the last few years, the weather had been pretty predictable, and Marceline had made the mistake of getting comfortable with it. When she had gone through her things to prepare for her move in with the skeletons, she had foolishly decided to donate a great deal of her “Boston-level winter” gear, forgetting that, at any time, the weather could turn their town into a landscape where cutting open a tauntaun seemed like the only feasible way to survive. 

Which, of course, it did, and she was caught without her favorite blanket to keep her warm. No matter how many socks she put on, or how many sweatshirts she stole, nothing worked quite as well as that old, worn out, itchy-as-sin blanket. 

She was putting away towels when she spotted something on the shelf above her, beneath a massive pile of various other sheet sets and blankets that only Papyrus could reach. Only a small strip of the navy-colored comforter was visible at her angle, but it immediately reminded her of her favorite winter blanket. With one foot on the bottom shelf and the other in the basket full of clean towels, she pulled herself up enough the get a better look at it. After a near miss with a potential fabric avalanche, she managed to dislodge the heavy blanket and jumped back into the hall to check it over. 

Five minutes later, Red jumped and dropped his bottle of mustard as he saw what he thought was River Person shuffle down the hall. Following the hooded figure, he found an amorphous blob consuming Marceline’s usual spot on the couch. One pale, fleshy hand protruded from a gap in the fabric with the remote, flipping through the movie options on the television.

Apparently, Marceline was cold. 

“You want me to turn up the heat?” He asked as he dropped down onto the cushion next to her. 

“No,” Her voice was muffled by the heavy fabric. “I’m good.” 

His quest for his favorite drink-condiment set aside, Red decided to settle into the couch, as Marceline finally selected Eureka. She set the remote down on the end table, and withdrew her hand into her cocoon, so that she was entirely contained beneath the blanket. 

For a while, he tried to get comfortable, but the heavy comforter consistently got in his way. His arm wasn’t long enough to get around it and settle over her shoulders, and even though he was pretty sure her feet were in their usual spot, he couldn’t feel her toes press against his femur the way they usually did. It was like trying to cuddle with an uncomfortably lumpy pillow – a lumpy pillow made out of burlap, no less, as all the little fabric pills made the old cotton incredibly itchy. Usually, he wouldn’t mind if he couldn’t cuddle with Marceline, because that happened all the time, but having his soulmate replaced with that miserable excuse for a blanket was downright intolerable. 

Marceline jumped when cold air invaded her warm little bubble. She turned to look at Red, knowing immediately he was at fault – although his eye lights were focused on the television, his hand had crept beneath the edge of the blanket, exposing her to the miserable chill of the house as his ice-cold fingers sought out her feet. She kicked him off, but he wasn’t deterred, grabbing for her ankle. 

“Why do you want me to suffer?” She whined, as she tried and failed to pull his phalanges loose, which only made him grin more. 

“C’mon, babe,” He grinned. “If you’re cold, we could always share body heat.” 

“You don’t have body heat.”

Completely ignoring her, Red grabbed the edge of the blanket and yanked it up. She shrieked unhappily as all the warmth she’d built up was ripped away, and tried to shuffle back as the frigid skeleton worked his way under her last line of defense against the misery that was winter. He wiggled into her blanket burrito, until the majority of his icy bulk had settled on top of her. His hands were crammed beneath not only her sweater, but her undershirt too, directly against her stomach, as if just to spite her – and knowing him, that was probably the case. 

“Damn it, Red, I was comfortable.” 

“Yeah,” He grinned. “But now we can be comfortable together.” 

He completely ignored her irritated huffing while he got comfortable, his head settled against her neck as he peered out through the little peep-hole she’d left in the blanket and pretended to watch the television. It was readily obvious he was pretending, too, as his hands began to slide up her ribs to skim the bottom of her breasts. Unable to feel the chill the same way she did, he had only worn basketball shorts and a heavy wife beater, and she could feel his magic already starting to settle at his pelvis, tingling but not yet taking form. It was the same sensation he left on her shoulder and throat, as his magic congealed into a sort of drool as he dragged his teeth across her skin.

“Not in the mood, Red.” She grunted, although he was far too heavy for her to dislodge him. “Try again after you’ve warmed up thirty degrees.” 

“That’s what I’ve got you for.” 

His fingers slid back down her sides, and crept beneath the waistband of her flannel pants. While he’d been gentle thus far, his fingers suddenly sank into the flesh of her ass to pull her pelvis up against his, where his magic had finally solidified. Although she considered rolling off the couch and making a break for it – Red was pushy, but he wouldn’t actually force her to do anything – he’d finally started to warm up, and his touch at least tolerable. The steady thrum of his magic didn’t hurt his case, either, a low, gentle vibration against her center. 

He’d won, and his grin said he knew it, as he pressed his teeth against her lips. His magical tongue worked its way into her mouth to find hers, her mouth flooded with a his not-quite-liquid drool that sparked pleasantly all the way down her throat. Never one to waste time, he dragged her pants and panties down in one smooth motion, one hand back beneath her sweater as he rocked slightly to get them over her socked feet. 

She tugged at the hem of his beater, until he pulled back just long enough for her to pull it over his head and drop it somewhere in the mess of fabric. A dim, red light filled the tiny space – it gleamed up his spine and across his hip bones from beneath his shorts, the same shade as the drooling tongue that lolled out of his mouth. It dripped onto her wool sweater and sank into the fabric, where it left a faint mark like little lightening bugs, then over her skin as he pushed the fabric up towards her throat. He lifted her by the back with one hand as he tugged it up with the other, until it was halfway over her head, and he lost interest now that her breasts were on display. She struggled out of it on her own, or tried to, as he shuffled down and lightly bit at her nipple, careful not to pierce her with the gold capped fang. 

“Jerk.” She huffed, and although he chuckled, he didn’t respond. 

Instead, he distracted her from her irritation. His drool trickled down her breast in a tingling trail that started to pool beneath her, while he plucked and pinched at her neglected nipple with his thumb and forefinger. 

Foreplay wasn’t his forte – and very rarely was it something she cared about, herself, so it suited her just fine when his mouth returned to her and his hand began to coast down her abdomen. One thin, bony finger split her lips, though only for a few brief moments, before that hand left her entirely, so he could tug his shorts down to his thighs. The magic that had collected at his pelvis glowed like a flashlight, formed into a human cock with a mysterious golden piercing at the underside of the head. 

He wrapped his phalanges around the impressive length as he settled over her and his pelvis gently pushed her thighs further apart. As much as she expected it, Marceline still jumped when she felt the unfettered magic against her sensitive flesh, and a surge of shock-like pleasure leaped through her muscles. It always reminded her of a vibrator on low, covered in stimulating lubricant, especially as he pressed his tip against her clit and coated her in a thin layer of his magic. 

“You ready, babe?” Red taunted, his already husky voice several octaves lower than normal. 

She rolled her eyes at him, and pulled his head up to press her lips against his teeth, his grin even wider as his pelvis shifted. He taunted her, and pulled back the moment he began to sink into her, over and over again. Normally, she wouldn’t mind his teasing, but a dim part of her mind was aware of the fact they were in the living room, and anyone could walk in at any time, so she wrapped her thighs around his hips and pressed her heels into his backside. Their awkward ball of limbs didn’t give him enough leverage to really resist as she pulled him closer, although his chuckle indicated he probably wouldn’t have if he could. 

A moan nearly broke out of her chest at the glorious sensation of being stretched apart. There was very little that compared to the sensation of fullness, especially as his magic sparked and thrummed against her walls. She settled her feet on the cushion between his femurs, the perfect angle for him to press against that spot on her front wall – and of course it was perfect, since as as skeleton, he could control every dimension of his magic, and he’d long ago found the exact shape to bring her the most pleasure. 

“Damn, beautiful,” He panted and drooled at the same time. “If you want me that bad, all ya had to do was say so.” 

“Just shut up and fuck me, Red.” 

“Yes, ma’am.” 

She was dimly aware of the cool air that swirled around them as he slid one foot out to find purchase on the floor, but it was a comforting change from the near oppressive heat she hadn’t quite noticed build up in their blanket fort. He shifted around with every thrust until her quiet, breathy sounds were interrupted by a soft moan as her legs spasmed against his bones and her fingers wrapped around his lower ribs. Electricity began to arc through her muscles with every thrust, her chest tight as he hit that spot with precision each time he filled her. 

With great effort, she managed to unravel one hand, and slid her fingertips through some of the magical drool that had begun to pool on her abdomen from his open mouth. His dim eye lights followed the movement as she quested further, to find her clit with the tips of two magic coated fingers. His long tongue lolled out of the side of his grin as she began to move them in quick, tiny circles, completely out of time with the motion of their hips. 

“That’s it, babe,” He panted, in spite of the fact he had no need to breathe. “Get yourself off on my cock.” 

In an effort to hush him – because it was the living room, in spite of the relatively privacy the blanket offered – she pulled his head down and sucked on the tip of his tongue. He chuckled, one hand squeezing her breast while his thumb flicked across the hardened tip as he began to move his hips in shorter, firmer motions. She could already feel sparks spread across her lower abdomen, intense one moment and absent the next, a distinct mark that she was close. Her right leg trembled out of control against him, and their blanket den was filled with not only the wet sound of their bodies as they moved together, but quiet grunts and moans. 

“Fuck,” She hissed as the sparks became more persistent, his thumb on top of her fingers, the pressure heavier than anything she’d ever normally apply to herself.

“You close?” He half-groaned, half-whispered, which earned a brief nod, her focus on the sensations that traveled down her legs to curl her toes. “So am I. Just need ya to set me off, beautiful.” 

The sparks evolved into fireworks, and the fireworks evolved into flames that spread across the space between her hip bones to light up every muscle in her body. Red groaned, loud and low, as his hips slowed considerably, but his thumb continued to press into her clit, while he rode through not only her orgasm but his own. A wave of cool, fluttering magic flooded through her, slowly absorbed into her flesh with a gentle thrum that warmed her soul in her chest. 

He didn’t pull out – his magic simply faded away, his pelvis pressed against hers as he settled on top of her, oddly boneless for a monster made exclusively out of magic bones. She was fine with this, for a few minutes, as she waited for her muscles to relax and her ability to breathe to return, but she became acutely aware that his leg was venting miserably cold air into her cozy nest, and that he was incredibly heavy. Red adamantly refused to budge while she shifted around, content to doze against her breast while she sought out her clothes, only to realize she couldn’t find them.

“Damn it, Red,” She hissed. “What the hell did you do with my pants?” 

“Right here.” 

The blanket down by her feet rose up to reveal Stretch, a smug look on his usually bored face. Marceline scrunched up her face as she glared at Red, who snickered but still refused to move, before she looked back as Stretch began to work his way beneath the blankets. His lanky form crawled up between her and the back of the couch, her pants in one hand, before he settled in beside her – and promptly shoved Red out of the blankets and onto the floor. 

“What the fuck was that for?” Came Red’s muffled snarl almost as soon as he hit the wooden panels with an incredible thud. 

“’s my turn.” Stretch yawned, his hand spread out across her abdomen, although he made no effort to stop her as she tugged on her pants and undershirt. “Now, you mind? I wanna get comforter-able with my girl.”


End file.
